1. Field of the Invention
The present invention relates to an air-conditioning apparatus including a compressor driven by a three-phase AC power supply.
2. Description of the Related Art
Rotary- and scroll-type compressors are known in the art which are driven by a three-phase AC power supply.
The use of the three-phase AC power supply sometimes causes a fault, such as a interphase short-circuiting and electrical disconnection. Upon the occurrence of such a defect, there arises a negative-phase sequence, that is, an unbalance of a phase current in the respective phase of the three-phase AC power supply.
Upon the arising of the negative-phase sequence, a torque as opposed to a normal torque is generated in a drive motor of a compressor, lowering the operation efficiency of the drive motor and hence generating an abnormal operation at the compressor.
In order to overcome such an inconvenience, a reverse rotation preventing device is provided, for example, in an air-conditioning apparatus shown in Published Unexamined Japanese Patent Application 1-114275.
That is, in this air-conditioning apparatus, a compressor 1 of the outdoor unit 11 is driven by a three-phase AC power supply 1a and the reverse rotation preventing device 10 is connected to the three-phase AC power supply 1a. The reverse rotation preventing device 11 detects the negative-phase sequence of the three-phase AC power supply 1a and serves to interrupt the power supply to the compressor 1.
The air-conditioning apparatus of the aforementioned Japanese Patent Application has the double function of interrupting the power supply to the compressor 1 and operating an alarm device 13.
In an apparatus as shown in Published Unexamined Japanese Patent Application 63-209426, a reverse rotation preventing device 17 is connected to a three-phase AC power supply. The reverse rotation preventing device 17 is comprised of a resistor 14, capacitor 15 and relay 16 and adapted to connect a motor 12 to a three-phase AC power supply through an energized relay when the three-phase AC power supply is in a positive-phase sequence and to disconnect the motor 12 from the three-phase AC power supply through the relay in deenergized state when the three-phase AC power supply is in a negative-phase sequence.
However, these reverse rotation preventing devices add to a cost on a finished apparatus.